Integrated oxide recess and floating gate fin trimming

ABSTRACT

Methods of etching back shallow trench isolation (STI) dielectric and trimming the exposed floating gate without breaking vacuum are described. The methods include recessing silicon oxide dielectric gapfill to expose vertical sidewalls of polysilicon floating gates. The exposed vertical sidewalls are then isotropically etched to evenly thin the polysilicon floating gates on the same substrate processing mainframe. Both recessing silicon oxide and isotropically etching polysilicon use remotely excited fluorine-containing apparatuses attached to the same mainframe to facilitate performing both operations without an intervening atmospheric exposure. An inter-poly dielectric may then be conformally deposited either on the same mainframe or outside the mainframe.

FIELD

Embodiments of the invention relate to floating flash gates and methodsof formation

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forremoval of exposed material. Chemical etching is used for a variety ofpurposes including transferring a pattern in photoresist into underlyinglayers, thinning layers or thinning lateral dimensions of featuresalready present on the surface. Often it is desirable to have an etchprocess which etches one material faster than another helping e.g. apattern transfer process proceed. Such an etch process is said to beselective of the first material. As a result of the diversity ofmaterials, circuits and processes, etch processes have been developedthat selectively remove one or more of a broad range of materials.

Dry etch processes are often desirable for selectively removing materialfrom semiconductor substrates. The desirability stems from the abilityto gently remove material from miniature structures with minimalphysical disturbance. Dry etch processes also allow the etch rate to beabruptly stopped by removing the gas phase reagents. Some dry-etchprocesses involve the exposure of a substrate to remote plasmaby-products formed from one or more precursors. For example, remoteplasma generation of nitrogen trifluoride in combination with ionsuppression techniques enables silicon oxide to be isotropically andselectively removed from a patterned substrate when the plasma effluentsare flowed into the substrate processing region.

Methods are needed to broaden the utility of selective dry isotropicetch processes.

SUMMARY

Methods of etching back shallow trench isolation (STI) dielectric andtrimming the exposed floating gate without breaking vacuum aredescribed. The methods include recessing silicon oxide dielectricgapfill to expose vertical sidewalls of polysilicon floating gates. Theexposed vertical sidewalls are then isotropically etched to evenly thinthe polysilicon floating gates on the same substrate processingmainframe. Both recessing silicon oxide and isotropically etchingpolysilicon use remotely excited fluorine-containing apparatusesattached to the same mainframe to facilitate performing both operationswithout an intervening atmospheric exposure. An inter-poly dielectricmay then be conformally deposited either on the same mainframe oroutside the mainframe.

Embodiments include methods of forming a floating gate. The methodsinclude transferring a patterned substrate into a substrate processingmainframe. The patterned substrate comprises two polysilicon floatinggates separated by shallow trench isolation silicon oxide gapfilldielectric. The two polysilicon floating gates each have verticalsidewalls. The methods further include transferring the patternedsubstrate into a first substrate processing chamber mounted on thesubstrate processing mainframe. The methods further include flowing afluorine-containing precursor and a hydrogen-containing precursor into afirst remote plasma region within the first substrate processing chamberwhile striking a plasma to form first plasma effluents from acombination of the fluorine-containing precursor and thehydrogen-containing precursor. The methods further include flowing thefirst plasma effluents into a first substrate processing region withinthe first substrate processing chamber. The first substrate processingregion houses the patterned substrate. The methods further includereacting the first plasma effluents with the shallow trench isolationsilicon oxide gapfill dielectric to form solid residue and sublimatingthe solid residue. Reacting the first plasma effluents includes loweringa top surface of the shallow trench isolation silicon oxide gapfilldielectric to below half the height of the two polysilicon floatinggates. The methods further include transferring the patterned substratefrom the first substrate processing chamber to a second substrateprocessing chamber mounted on the substrate processing mainframe. Themethods further include flowing a fluorine-containing precursor into asecond remote plasma region within the second substrate processingchamber while striking a plasma to form second plasma effluents andflowing the second plasma effluents through a showerhead into a secondsubstrate processing region housing the patterned substrate within thesecond substrate processing chamber. The methods further includeisotropically etching the two polysilicon floating gates to thin theirwidth and form sidewalls which are again vertical. The methods furtherinclude removing the patterned substrate from the substrate processingmainframe. The patterned substrate is not exposed to atmosphere betweentransferring the patterned substrate into the substrate processingmainframe and removing the patterned substrate from the substrateprocessing mainframe.

Embodiments include methods of forming a floating gate. The methodsinclude transferring a patterned substrate into a substrate processingmainframe. The patterned substrate comprises two polysilicon floatinggates separated by shallow trench isolation silicon oxide gapfilldielectric. The two polysilicon floating gates each have verticalsidewalls. The methods further include transferring the patternedsubstrate into a first substrate processing chamber mounted on thesubstrate processing mainframe. The methods further include flowing afluorine-containing precursor into a first remote plasma region withinthe first substrate processing chamber while striking a plasma to formfirst plasma effluents from a combination of the fluorine-containingprecursor. The methods further include flowing the plasma effluents intoa first substrate processing region within the first substrateprocessing chamber. The first substrate processing region houses thepatterned substrate. The methods further include flowing an unexcitedprecursor directly into the first substrate processing region withoutfirst passing the unexcited precursor through any plasma prior toentering the first substrate processing region. The methods furtherinclude reacting the plasma effluents with the shallow trench isolationsilicon oxide gapfill dielectric. Reacting the plasma effluentscomprises reducing a top surface of the shallow trench isolation siliconoxide gapfill dielectric to below half the height of the two polysiliconfloating gates. The methods further include transferring the patternedsubstrate from the first substrate processing chamber to a secondsubstrate processing chamber mounted on the substrate processingmainframe. The methods further include flowing a fluorine-containingprecursor into a second remote plasma region within the second substrateprocessing chamber while striking a plasma to form second plasmaeffluents and flowing the plasma effluents through a showerhead into asecond substrate processing region housing the patterned substratewithin the second substrate processing chamber. The methods furtherinclude isotropically etching the two polysilicon floating gates toreduce from an initial floating gate width to a final floating gatewidth and form sidewalls which are again essentially vertical. Themethods further include removing the patterned substrate from thesubstrate processing mainframe. The patterned substrate is not exposedto atmosphere between transferring the patterned substrate into thesubstrate processing mainframe and removing the patterned substrate fromthe substrate processing mainframe.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosed embodiments. The features andadvantages of the disclosed embodiments may be realized and attained bymeans of the instrumentalities, combinations, and methods described inthe specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodimentsmay be realized by reference to the remaining portions of thespecification and the drawings.

FIGS. 1A, 1B, 1C and 1D are cross-sectional views of a patternedsubstrate during an integrated etch process according to embodiments.

FIG. 2 is a flow chart of an integrated etch process according toembodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processingchamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a portion of asubstrate processing chamber according to embodiments.

FIG. 3C shows a bottom plan view of a showerhead according toembodiments.

FIG. 4 shows a top plan view of an exemplary substrate processing systemaccording to embodiments.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

Methods of etching back shallow trench isolation (STI) dielectric andtrimming the exposed floating gate without breaking vacuum aredescribed. The methods include recessing silicon oxide dielectricgapfill to expose vertical sidewalls of polysilicon floating gates. Theexposed vertical sidewalls are then isotropically etched to evenly thinthe polysilicon floating gates on the same substrate processingmainframe. Both recessing silicon oxide and isotropically etchingpolysilicon use remotely excited fluorine-containing apparatusesattached to the same mainframe to facilitate performing both operationswithout an intervening atmospheric exposure. An inter-poly dielectricmay then be conformally deposited either on the same mainframe oroutside the mainframe.

Recently-developed gas-phase remote etch processes have been designed,in part, to remove the need to expose delicate surface patterns toliquid etchants. Liquid etchants are increasingly responsible forcollapsing delicate surface patterns as linewidths are reduced. Furtherimprovements in yields, performance and cost reduction are enabled bythe methods presented herein. The methods involve performing severaloperations in the same substrate processing mainframe with multiplesubstrate processing chambers attached, generally around the perimeterof the mainframe. All semiconductor process chambers may be under vacuumaside from the process gases periodically introduced to treat asubstrate. Prior art liquid etch processes are not candidates for suchintegration and so new process flows are now possible.

In order to better understand and appreciate embodiments of theinvention, reference is now made to FIGS. 1A, 1B, 1C and 1D which arecross-sectional views of a flash memory cell during a method 201 (seeFIG. 2) of forming the flash memory cells according to embodiments. Inone example, a flash memory cell on patterned substrate 101 comprisesgapfill silicon oxide 105-1, tunnel oxide 115 and floating gate 120-1.The flash memory cell depicted is sliced along the bitline direction ineach view of FIGS. 1A, 1B, 1C and 1D. Chemical mechanical polishing(CVD) may have been performed prior to the view of FIG. 1A and the topof gapfill silicon oxide 105-1 may be flush with the top of floatinggate 120-1 in embodiments. “Top” and “Up” will be used herein todescribe portions/directions perpendicularly distal from the substrateplane and further away from the center of mass of the substrate in theperpendicular direction. “Vertical” will be used to describe itemsaligned in the “Up” direction towards the “Top”.

The shallow trench depicted in each of FIGS. 1A-D may have a width lessthan or about 15 nm or less than or about 13 nm according toembodiments. Tunnel oxide 115 may comprise or consist of silicon oxidein embodiments. Floating gate 120-1 may comprise or consist of dopedpolysilicon according to embodiments.

Patterned substrate 101 as shown in FIG. 1A is delivered into asubstrate processing system (e.g. a single substrate processingmainframe) having multiple substrate processing chambers affixed andevacuated prior to transfer. Patterned substrate 101 is transferred intoa first substrate processing region within a first substrate processingchamber (operation 210) to initiate method 201 of forming a flash memorycell. A flow of nitrogen trifluoride is then introduced into a firstremote plasma region where the nitrogen trifluoride is excited in aremote plasma struck within the separate plasma region. A separateplasma region may be referred to as a remote plasma region herein andmay be within a distinct module from the processing chamber or acompartment within the processing chamber separated from the substrateprocessing region by an aperture or a showerhead. In general, afluorine-containing precursor may be flowed into the remote plasmaregion and the fluorine-containing precursor comprises at least oneprecursor selected from the group consisting of atomic fluorine,diatomic fluorine, bromine trifluoride, chlorine trifluoride, nitrogentrifluoride, hydrogen fluoride, fluorinated hydrocarbons, sulfurhexafluoride and xenon difluoride.

According to embodiments, the plasma effluents may pass through ashowerhead and/or ion suppressor to reduce the electron temperature (toreduce the ion concentration) in the substrate processing region.Reduced electron temperatures as described subsequently herein have beenfound to increase the etch selectivity of gapfill silicon oxide comparedto other exposed materials (e.g. polysilicon). The low electrontemperatures are described later in the specification (e.g. <0.5 eV).Electron temperatures do not need to be this low if ahydrogen-containing precursor, such as ammonia, is also present in thefirst remote plasma region during operation 220.

In embodiments, a hydrogen-containing precursor, ammonia, may besimultaneously flowed into the first remote plasma region along with thenitrogen trifluoride described previously. The hydrogen-containingprecursor may be flowed into the first remote plasma region duringoperation 220. Generally speaking, the hydrogen-containing precursor mayinclude one or more of atomic hydrogen, molecular hydrogen, ammonia, ahydrocarbon and an incompletely halogen-substituted hydrocarbon.

Alternatively, an unexcited precursor may be flowed directly into thefirst substrate processing region without first passing the unexcitedprecursor through any plasma prior to entering the first substrateprocessing region. The unexcited precursor may be excited only by theplasma effluents formed in the first remote plasma region. The unexcitedprecursor may be water or an alcohol (each of which contains an OHgroup) in embodiments. The unexcited precursor may also be NxHy (with xand y each greater than or equal to one), may be flowed directly intofirst substrate processing region without prior plasma excitation. Forexample, the unexcited precursor may be ammonia in embodiments. Thepresence of the unexcited precursor just described may increase siliconoxide selectivity for etch operation 220. As before, the plasmaeffluents may pass through a showerhead and/or ion suppressor to reducethe electron temperature (to reduce the ion concentration) in thesubstrate processing region prior to combination with unexcited NxHy orOH group precursor. Reduced electron temperatures as describedsubsequently herein have been found to increase the etch selectivity ofgapfill silicon oxide relative to other exposed materials, such aspolysilicon.

Formed by the various means presented above, the plasma effluents formedin the remote plasma region are then flowed into the substrateprocessing region and patterned substrate 101 is selectively etched inoperation 230 of method 201. Operation 230 (and all etches describedherein) may be referred to as a gas-phase etch to highlight the contrastwith liquid etch processes. The plasma effluents may enter the substrateprocessing region through through-holes in a showerhead or another styleof aperture which separates the remote plasma region from the substrateprocessing region. In operation 230, gapfill silicon oxide 105-1 isremoved at a much higher rate than floating gate 120-1 to lower the topinterface and form gapfill silicon oxide 105-2 without altering thevertical nature of the walls of floating gate 120-1. The reactivechemical species are removed from the substrate processing region.

FIG. 1B shows a remaining portion, gapfill silicon oxide 105-2,indicating partial removal of gapfill silicon oxide 105-1. Inembodiments, the gapfill silicon oxide 105-2 may have a gas-SiO2interface located below half the height of floating gate 120-1. Thegas-SiO2 interface may also be referred to as the top of gapfill siliconoxide 105-2 as viewed in, e.g., FIG. 1B. The top of patterned substrate101 is also shown in FIG. 1B and patterned substrate may be activesingle-crystal silicon which participates in the writing, reading anderasing of a flash cell by transferring charge to or from floating gate120-1. The top of gapfill silicon oxide 105-2 may be less than 30 nmhigher than the top of patterned substrate 101 as measured in thevertical dimension. The top of gapfill silicon oxide 105-2 may be lessthan 30 nm higher, less than 25 nm higher or less than 20 nm higher thanthe top of patterned substrate 101 according to embodiments.

Operation 220 may include applying energy to the fluorine-containingprecursor while in the remote plasma region to generate the plasmaeffluents. As would be appreciated by one of ordinary skill in the art,the plasma may include a number of charged and neutral species includingradicals and ions. The plasma may be generated using known techniques(e.g., radio frequency excitations, capacitively-coupled power orinductively coupled power). In an embodiment, the energy is appliedusing a capacitively-coupled plasma unit. The remote plasma source powermay be between about 5 watts and about 5000 watts, between about 25watts and about 1500 watts or between about 50 watts and about 1000watts according to embodiments. The pressure in the remote plasma regionmay be such that the pressure in the substrate processing region ends upbetween about 0.01 Torr and about 50 Torr or between about 0.1 Torr andabout 5 Torr in embodiments. The capacitively-coupled plasma unit may bedisposed remote from a substrate processing region of the processingchamber. For example, the capacitively-coupled plasma unit and theplasma generation region may be separated from the gas reaction regionby a showerhead. All process parameters for the gapfill silicon oxideetch operation described herein apply to all remote plasma embodimentsherein unless otherwise indicated. Other plasma parameters will bedescribed in the exemplary equipment section.

Including a hydrogen-containing precursor with the fluorine-containingprecursor in the first remote plasma region creates plasma effluentswhich produce solid etch by-products while etching gapfill silicon oxide105-1. The solid etch by-products form on the surface when the patternedsubstrate temperature is less than 80° C., less than 70° C. or less than60° C. in embodiments. In this case, the solid etch by-products may beremoved by sublimation effected by raising the patterned substratetemperature above 80° C., 90° C. or 100° C. according to embodiments. Inorder to remove the desired amount, the exposure to plasma effluentsfollowed by sublimation may be repeated an integral number of times. Theexposure to plasma effluents followed by sublimation may occur at leastone, two, three, or four times, in embodiments. Lower remote plasmapowers have been found to be effective when using hydrogen-containingprecursor in addition to the fluorine-containing precursor in the firstremote plasma region. The remote plasma source power may be betweenabout 0.5 watts and about 500 watts, between about 3 watts and about 150watts or between about 10 watts and about 100 watts according toembodiments.

Patterned substrate 101 is removed from first substrate processingregion and placed in a second substrate processing region within asecond substrate processing chamber affixed to the same substrateprocessing mainframe in operation 230. An air-tight seal is maintainedbetween the atmosphere outside the substrate processing mainframe andthe interior of substrate processing mainframe during operation 240, atrait which may also be referred to as transferring “without breakingvacuum”. Avoiding atmospheric exposure prevents the formation of anative oxide. A native oxide surrounding polysilicon floating gate 120-1would discourage or completely prevent the thinning of polysiliconfloating gate 120-1 in the next stage because of the high etchselectivity of polysilicon compared to silicon oxide. As a consequence,avoiding breaking vacuum allows enhanced control of the location of thetop surface of gapfill silicon oxide 105-2.

A flow of nitrogen trifluoride is then introduced into a second remoteplasma region inside the second substrate processing region where thenitrogen trifluoride is excited in a second remote plasma struck withinthe second remote plasma region. Remote plasma parameters may be thesame embodiments described for operation 220 and in the exemplaryequipment section. In general, a fluorine-containing precursor may beflowed into the second remote plasma region and the fluorine-containingprecursor comprises at least one precursor selected from the groupconsisting of atomic fluorine, diatomic fluorine, bromine trifluoride,chlorine trifluoride, nitrogen trifluoride, hydrogen fluoride,fluorinated hydrocarbons, sulfur hexafluoride and xenon difluoride.Plasma effluents are formed and passed into a second substrateprocessing region (operation 250) now housing patterned substrate 101. Aportion of floating gate 120-1 (e.g. polysilicon floating gate) isremoved in operation 260 to thin the horizontal dimension of floatinggate 120-2 as shown in FIG. 1C. Each sidewall of the floating gate 120-2is within 2° of vertical in embodiments. Operation 260 reduces the widthof floating gate 120-1 from an initial floating gate width to a finalfloating gate width 120-2 and the final floating gate width may be lessthan 80% of the initial floating gate width in embodiments. Unusedprocess effluents are removed from the second substrate processingregion and patterned substrate 101 is removed from the second substrateprocessing region and then removed from the substrate processingmainframe (operation 270). A conformal inter-poly dielectric layer maythen be deposited on patterned substrate 101 to coat the thinnedfloating gate 120-2 as shown in FIG. 1D.

The second remote plasma region may be devoid or essentially devoid ofhydrogen to achieve high selectivity of polysilicon relative to siliconoxide during operations 250 and 260. Independently or in combinationwith being hydrogen-free, the second remote plasma region may be devoidof oxygen, in embodiments, during operations 250 and 260, to achieve thehigh selectivities of polysilicon relative to gapfill silicon oxide asdescribed herein. As before, the plasma effluents may pass through ashowerhead and/or ion suppressor to reduce the electron temperature (toreduce the ion concentration) in the substrate processing region.Reduced electron temperatures as described subsequently herein have beenfound to increase the etch selectivity of gapfill polysilicon relativeto other exposed materials.

All plasmas described herein may further include one or more relativelyinert gases such as He, N₂, Ar. The inert gas can be used to improveplasma stability or process uniformity. Argon is helpful, as anadditive, to promote the formation of a stable plasma. Processuniformity is generally increased when helium is included. Theseadditives are present in embodiments throughout this specification. Flowrates and ratios of the different gases may be used to control etchrates and etch selectivity.

In all relevant operations (e.g. 220 and 250) embodiments describedherein, the fluorine-containing gas (e.g. NF₃) is supplied at a flowrate of between about 5 sccm (standard cubic centimeters per minute) and400 sccm, He at a flow rate of between about 0 slm (standard liters perminute) and 3 slm, and N₂ at a flow rate of between about 0 slm and 3slm. One of ordinary skill in the art would recognize that other gasesand/or flows may be used depending on a number of factors includingprocessing chamber configuration, substrate size and geometry and layoutof features being etched. In addition to the other embodiments describedherein, the pressure in the remote plasma region and/or the substrateprocessing region during all selective etch processes may be betweenabout 0.01 Torr and about 30 Torr or between about 1 Torr and about 5Torr in embodiments. The remote plasma region is disposed remote fromthe substrate processing region. The remote plasma region is fluidlycoupled to the substrate processing region and both regions may be atroughly the same pressure during processing.

The temperature of the substrate may be between about −20° C. and about200° C. during gapfill silicon oxide selective etch and selective etchoperations later in the process. The patterned substrate temperature mayalso be maintained at between −10° C. and about 50° C. or between about5° C. and about 25° C. during the gas-phase etching processes disclosedherein. Performing etching operations 230 and 260 at theseextraordinarily low temperatures avoids outdiffusion of boron (oranother dopant) from polysilicon floating gate 120-1 and 120-2. Priorart techniques for recessing STI gapfill may involve reactive ionetching (RIE) after which ashing is performed to remove the mask. Ashingis typically carried out at around 300° C. which would allow dopants(especially boron) to diffuse within and from the polysilicon floatinggate. The dopants would need to be replenished in prior art processesbut not using the methods described herein. Replenishing dopants mayalso be referred to as counter-doping.

In embodiments, an ion suppressor (which may be the showerhead) may beused to provide radical and/or neutral species for gas-phase etching.The ion suppressor may also be referred to as an ion suppressionelement. In embodiments, for example, the ion suppressor is used tofilter etching plasma effluents (including radical-fluorine) en routefrom the remote plasma region to the substrate processing region. Theion suppressor may be used to provide a reactive gas having a higherconcentration of radicals than ions. Plasma effluents pass through theion suppressor disposed between the remote plasma region and thesubstrate processing region. The ion suppressor functions todramatically reduce or substantially eliminate ionic species travelingfrom the plasma generation region to the substrate. The ion suppressorsdescribed herein are simply one way to achieve a low electrontemperature in the substrate processing region during the gas-phase etchprocesses described herein.

In embodiments, an electron beam is passed through the substrateprocessing region in a plane parallel to the substrate to reduce theelectron temperature of the plasma effluents. A simpler showerhead maybe used if an electron beam is applied in this manner. The electron beammay be passed as a laminar sheet disposed above the substrate inembodiments. The electron beam provides a source of neutralizingnegative charge and provides a more active means for reducing the flowof positively charged ions towards the substrate and increasing theselectivity of silicon nitride in embodiments. The flow of plasmaeffluents and various parameters governing the operation of the electronbeam may be adjusted to lower the electron temperature measured in thesubstrate processing region.

The electron temperature may be measured using a Langmuir probe in thesubstrate processing region during excitation of a plasma in the remoteplasma. In embodiments, the electron temperature may be less than 0.5eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV. Theseextremely low values for the electron temperature are enabled by thepresence of the electron beam, showerhead and/or the ion suppressor.Uncharged neutral and radical species may pass through the electron beamand/or the openings in the ion suppressor to react at the substrate.Such a process using radicals and other neutral species can reduceplasma damage compared to conventional plasma etch processes thatinclude sputtering and bombardment. Embodiments of the present inventionare also advantageous over conventional wet etch processes where surfacetension of liquids can cause bending and peeling of small features.

The substrate processing region may be described herein as “plasma-free”during the etch processes described herein. “Plasma-free” does notnecessarily mean the region is devoid of plasma. Ionized species andfree electrons created within the plasma region may travel through pores(apertures) in the partition (showerhead) at exceedingly smallconcentrations. The borders of the plasma in the chamber plasma regionare hard to define and may encroach upon the substrate processing regionthrough the apertures in the showerhead. Furthermore, a low intensityplasma may be created in the substrate processing region withouteliminating desirable features of the etch processes described herein.All causes for a plasma having much lower intensity ion density than thechamber plasma region during the creation of the excited plasmaeffluents do not deviate from the scope of “plasma-free” as used herein.

The etch selectivities during the silicon oxide etches described herein(silicon oxide:polysilicon) may be greater than or about 300:1, greaterthan or about 500:1, greater than or about 750:1, or greater than orabout 1000:1 in embodiments. A higher the etch selectivity of siliconoxide relative to polysilicon results in an increasing vertical wall forfloating gate 120-1 after following completion of the method 201 ofmaking flash memory cells. For the polysilicon etching operations, theetch selectivity of polysilicon to silicon oxide may be greater than orabout 700:1, greater than or about 1000:1, greater than or about 2000:1,greater than or about 3000:1 or essentially infinite according toembodiments. The etch selectivity of polysilicon relative to siliconoxide should be very high to control the height of gapfill silicon oxide105-2 which determines the performance and reliability of the flashmemory devices.

Additional process parameters are disclosed in the course of describingan exemplary processing chamber and system.

Exemplary Processing System

FIG. 3A shows a cross-sectional view of an exemplary substrateprocessing chamber 1001 with partitioned plasma generation regionswithin the processing chamber. During film etching, e.g., silicon oxideor polysilicon, etc., a process gas may be flowed into chamber plasmaregion 1015 through a gas inlet assembly 1005. A remote plasma system(RPS) 1002 may optionally be included in the system, and may process afirst gas which then travels through gas inlet assembly 1005. The inletassembly 1005 may include two or more distinct gas supply channels wherethe second channel (not shown) may bypass the RPS 1002, if included.Accordingly, in embodiments the precursor gases may be delivered to theprocessing chamber in an unexcited state. In another example, the firstchannel provided through the RPS may be used for the process gas and thesecond channel bypassing the RPS may be used for a treatment gas inembodiments. The process gas may be excited within the RPS 1002 prior toentering the chamber plasma region 1015. Accordingly, thefluorine-containing precursor as discussed above, for example, may passthrough RPS 1002 or bypass the RPS unit in embodiments. Various otherexamples encompassed by this arrangement will be similarly understood.

A cooling plate 1003, faceplate 1017, ion suppressor 1023, showerhead1025, and a substrate support 1065 (also known as a pedestal), having asubstrate 1055 disposed thereon, are shown and may each be includedaccording to embodiments. The pedestal 1065 may have a heat exchangechannel through which a heat exchange fluid flows to control thetemperature of the substrate. This configuration may allow the substrate1055 temperature to be cooled or heated to maintain relatively lowtemperatures, such as between about −20° C. to about 200° C., ortherebetween. The heat exchange fluid may comprise ethylene glycoland/or water. The wafer support platter of the pedestal 1065, which maycomprise aluminum, ceramic, or a combination thereof, may also beresistively heated to relatively high temperatures, such as from up toor about 100° C. to above or about 1100° C., using an embedded resistiveheater element. The heating element may be formed within the pedestal asone or more loops, and an outer portion of the heater element may runadjacent to a perimeter of the support platter, while an inner portionruns on the path of a concentric circle having a smaller radius. Thewiring to the heater element may pass through the stem of the pedestal1065, which may be further configured to rotate.

The faceplate 1017 may be pyramidal, conical, or of another similarstructure with a narrow top portion expanding to a wide bottom portion.The faceplate 1017 may additionally be flat as shown and include aplurality of through-channels used to distribute process gases. Plasmagenerating gases and/or plasma excited species, depending on use of theRPS 1002, may pass through a plurality of holes, shown in FIG. 3B, infaceplate 1017 for a more uniform delivery into the chamber plasmaregion 1015.

Exemplary configurations may include having the gas inlet assembly 1005open into a gas supply region 1058 partitioned from the chamber plasmaregion 1015 by faceplate 1017 so that the gases/species flow through theholes in the faceplate 1017 into the chamber plasma region 1015.Structural and operational features may be selected to preventsignificant backflow of plasma from the chamber plasma region 1015 backinto the supply region 1058, gas inlet assembly 1005, and fluid supplysystem 1010. The structural features may include the selection ofdimensions and cross-sectional geometries of the apertures in faceplate1017 to deactivate back-streaming plasma. The operational features mayinclude maintaining a pressure difference between the gas supply region1058 and chamber plasma region 1015 that maintains a unidirectional flowof plasma through the showerhead 1025. The faceplate 1017, or aconductive top portion of the chamber, and showerhead 1025 are shownwith an insulating ring 1020 located between the features, which allowsan AC potential to be applied to the faceplate 1017 relative toshowerhead 1025 and/or ion suppressor 1023. The insulating ring 1020 maybe positioned between the faceplate 1017 and the showerhead 1025 and/orion suppressor 1023 enabling a capacitively coupled plasma (CCP) to beformed in the first plasma region. A baffle (not shown) may additionallybe located in the chamber plasma region 1015, or otherwise coupled withgas inlet assembly 1005, to affect the flow of fluid into the regionthrough gas inlet assembly 1005.

The ion suppressor 1023 may comprise a plate or other geometry thatdefines a plurality of apertures throughout the structure that areconfigured to suppress the migration of ionically-charged species out ofchamber plasma region 1015 while allowing uncharged neutral or radicalspecies to pass through the ion suppressor 1023 into an activated gasdelivery region between the suppressor and the showerhead. Inembodiments, the ion suppressor 1023 may comprise a perforated platewith a variety of aperture configurations. These uncharged species mayinclude highly reactive species that are transported with less reactivecarrier gas through the apertures. As noted above, the migration ofionic species through the holes may be reduced, and in some instancescompletely suppressed. Controlling the amount of ionic species passingthrough the ion suppressor 1023 may provide increased control over thegas mixture brought into contact with the underlying wafer substrate,which in turn may increase control of the deposition and/or etchcharacteristics of the gas mixture. For example, adjustments in the ionconcentration of the gas mixture can significantly alter its etchselectivity, e.g., SiO:Si etch ratios, Si:SiO etch ratios, etc.

The plurality of holes in the ion suppressor 1023 may be configured tocontrol the passage of the activated gas, i.e., the ionic, radical,and/or neutral species, through the ion suppressor 1023. For example,the aspect ratio of the holes, or the hole diameter to length, and/orthe geometry of the holes may be controlled so that the flow ofionically-charged species in the activated gas passing through the ionsuppressor 1023 is reduced. The holes in the ion suppressor 1023 mayinclude a tapered portion that faces chamber plasma region 1015, and acylindrical portion that faces the showerhead 1025. The cylindricalportion may be shaped and dimensioned to control the flow of ionicspecies passing to the showerhead 1025. An adjustable electrical biasmay also be applied to the ion suppressor 1023 as an additional means tocontrol the flow of ionic species through the suppressor.

The ion suppression element 1023 may function to reduce or eliminate theamount of ionically charged species traveling from the plasma generationregion to the substrate. Uncharged neutral and radical species may stillpass through the openings in the ion suppressor to react with thesubstrate.

Showerhead 1025 in combination with ion suppressor 1023 may allow aplasma present in chamber plasma region 1015 to avoid directly excitinggases in substrate processing region 1033, while still allowing excitedspecies to travel from chamber plasma region 1015 into substrateprocessing region 1033. In this way, the chamber may be configured toprevent the plasma from contacting a substrate 1055 being etched. Thismay advantageously protect a variety of intricate structures and filmspatterned on the substrate, which may be damaged, dislocated, orotherwise warped if directly contacted by a generated plasma.Additionally, when plasma is allowed to contact the substrate orapproach the substrate level, the rate at which silicon oxide orpolysilicon etch may increase.

The processing system may further include a power supply 1040electrically coupled with the processing chamber to provide electricpower to the faceplate 1017, ion suppressor 1023, showerhead 1025,and/or pedestal 1065 to generate a plasma in the chamber plasma region1015 or processing region 1033. The power supply may be configured todeliver an adjustable amount of power to the chamber depending on theprocess performed. Such a configuration may allow for a tunable plasmato be used in the processes being performed. Unlike a remote plasmaunit, which is often presented with on or off functionality, a tunableplasma may be configured to deliver a specific amount of power tochamber plasma region 1015. This in turn may allow development ofparticular plasma characteristics such that precursors may bedissociated in specific ways to enhance the etching profiles produced bythese precursors.

A plasma may be ignited either in chamber plasma region 1015 aboveshowerhead 1025 or substrate processing region 1033 below showerhead1025. A plasma may be present in chamber plasma region 1015 to producethe radical-fluorine precursors from an inflow of thefluorine-containing precursor. An AC voltage typically in the radiofrequency (RF) range may be applied between the conductive top portionof the processing chamber, such as faceplate 1017, and showerhead 1025and/or ion suppressor 1023 to ignite a plasma in chamber plasma region1015 during deposition. An RF power supply may generate a high RFfrequency of 13.56 MHz but may also generate other frequencies alone orin combination with the 13.56 MHz frequency.

Plasma power can be of a variety of frequencies or a combination ofmultiple frequencies. In the exemplary processing system the plasma maybe provided by RF power delivered to faceplate 1017 relative to ionsuppressor 1023 and/or showerhead 1025. The RF power may be betweenabout 10 watts and about 5000 watts, between about 100 watts and about2000 watts, between about 200 watts and about 1500 watts, or betweenabout 200 watts and about 1000 watts in embodiments. The RF frequencyapplied in the exemplary processing system may be low RF frequenciesless than about 200 kHz, high RF frequencies between about 10 MHz andabout 15 MHz, or microwave frequencies greater than or about 1 GHz inembodiments. The plasma power may be capacitively-coupled (CCP) orinductively-coupled (ICP) into the remote plasma region.

Chamber plasma region 1015 (top plasma in figure) may be left at low orno power when a bottom plasma in the substrate processing region 1033 isturned on to, for example, cure a film or clean the interior surfacesbordering substrate processing region 1033. A plasma in substrateprocessing region 1033 may be ignited by applying an AC voltage betweenshowerhead 1025 and the pedestal 1065 or bottom of the chamber. Atreatment gas (such as argon) may be introduced into substrateprocessing region 1033 while the plasma is present to facilitatetreatment of the patterned substrate. The showerhead 1025 may also bebiased at a positive DC voltage relative to the pedestal 1065 or bottomof the chamber to accelerate positively charged ions toward patternedsubstrate 1055. In embodiments, the local plasma in substrate processingregion 1033 may be struck by applying AC power via aninductively-coupled source while applying DC power by capacitivelycoupled means. As indicated previously, the local plasma power may bebetween about 10 watts and about 500 watts, between about 20 watts andabout 400 watts, between about 30 watts and about 300 watts, or betweenabout 50 watts and about 200 watts in embodiments.

A fluid, such as a precursor, for example a fluorine-containingprecursor, may be flowed into the processing region 1033 by embodimentsof the showerhead described herein. Excited species derived from theprocess gas in chamber plasma region 1015 may travel through aperturesin the ion suppressor 1023, and/or showerhead 1025 and react with anadditional precursor flowing into the processing region 1033 from aseparate portion of the showerhead. Alternatively, if all precursorspecies are being excited in chamber plasma region 1015, no additionalprecursors may be flowed through the separate portion of the showerhead.Little or no plasma may be present in the processing region 1033 duringthe remote plasma etch process. Excited derivatives of the precursorsmay combine in the region above the substrate and/or on the substrate toetch structures or remove species from the substrate.

Exciting the fluids in the chamber plasma region 1015 directly, orexciting the fluids in the RPS units 1002, may provide several benefits.The concentration of the excited species derived from the fluids may beincreased within the processing region 1033 due to the plasma in thechamber plasma region 1015. This increase may result from the locationof the plasma in the chamber plasma region 1015. The processing region1033 may be located closer to the chamber plasma region 1015 than theremote plasma system (RPS) 1002, leaving less time for the excitedspecies to leave excited states through collisions with other gasmolecules, walls of the chamber, and surfaces of the showerhead.

The uniformity of the concentration of the excited species derived fromthe process gas may also be increased within the processing region 1033.This may result from the shape of the chamber plasma region 1015, whichmay be more similar to the shape of the processing region 1033. Excitedspecies created in the RPS 1002 may travel greater distances to passthrough apertures near the edges of the showerhead 1025 relative tospecies that pass through apertures near the center of the showerhead1025. The greater distance may result in a reduced excitation of theexcited species and, for example, may result in a slower growth ratenear the edge of a substrate. Exciting the fluids in the chamber plasmaregion 1015 may mitigate this variation for the fluid flowed through RPS1002, or alternatively bypassed around the RPS unit.

The processing gases may be excited in chamber plasma region 1015 andmay be passed through the showerhead 1025 to the processing region 1033in the excited state. While a plasma may be generated in the processingregion 1033, a plasma may alternatively not be generated in theprocessing region. In one example, the only excitation of the processinggas or precursors may be from exciting the processing gases in chamberplasma region 1015 to react with one another in the processing region1033. As previously discussed, this may be to protect the structurespatterned on the substrate 1055.

In addition to the fluid precursors, there may be other gases introducedat varied times for varied purposes, including carrier gases to aiddelivery. A treatment gas may be introduced to remove unwanted speciesfrom the chamber walls, the substrate, the deposited film and/or thefilm during deposition. A treatment gas may be excited in a plasma andthen used to reduce or remove residual content inside the chamber. Insome embodiments the treatment gas may be used without a plasma. Whenthe treatment gas includes water vapor, the delivery may be achievedusing a mass flow meter (MFM), an injection valve, or by commerciallyavailable water vapor generators. The treatment gas may be introduced tothe processing region 1033, either through the RPS unit or bypassing theRPS unit, and may further be excited in the first plasma region.

FIG. 3B shows a detailed view of the features affecting the processinggas distribution through faceplate 1017. As shown in FIG. 3A and FIG.3B, faceplate 1017, cooling plate 1003, and gas inlet assembly 1005intersect to define a gas supply region 1058 into which process gasesmay be delivered from gas inlet 1005. The gases may fill the gas supplyregion 1058 and flow to chamber plasma region 1015 through apertures1059 in faceplate 1017. The apertures 1059 may be configured to directflow in a substantially unidirectional manner such that process gasesmay flow into processing region 1033, but may be partially or fullyprevented from backflow into the gas supply region 1058 after traversingthe faceplate 1017.

The gas distribution assemblies such as showerhead 1025 for use in theprocessing chamber section 1001 may be referred to as dual channelshowerheads (DCSH) and are additionally detailed in the embodimentsdescribed in FIG. 3A as well as FIG. 3C herein. The dual channelshowerhead may provide for etching processes that allow for separationof etchants outside of the processing region 1033 to provide limitedinteraction with chamber components and each other prior to beingdelivered into the processing region.

The showerhead 1025 may comprise an upper plate 1014 and a lower plate1016. The plates may be coupled with one another to define a volume 1018between the plates. The coupling of the plates may be so as to providefirst fluid channels 1019 through the upper and lower plates, and secondfluid channels 1021 through the lower plate 1016. The formed channelsmay be configured to provide fluid access from the volume 1018 throughthe lower plate 1016 via second fluid channels 1021 alone, and the firstfluid channels 1019 may be fluidly isolated from the volume 1018 betweenthe plates and the second fluid channels 1021. The volume 1018 may befluidly accessible through a side of the gas distribution assembly 1025.Although the exemplary system of FIGS. 3A-3C includes a dual-channelshowerhead, it is understood that alternative distribution assembliesmay be utilized that maintain first and second precursors fluidlyisolated prior to the processing region 1033. For example, a perforatedplate and tubes underneath the plate may be utilized, although otherconfigurations may operate with reduced efficiency or not provide asuniform processing as the dual-channel showerhead as described.

In the embodiment shown, showerhead 1025 may distribute via first fluidchannels 1019 process gases which contain plasma effluents uponexcitation by a plasma in chamber plasma region 1015. In embodiments,the process gas introduced into the RPS 1002 and/or chamber plasmaregion 1015 may contain fluorine, e.g., CF₄, NF₃ or XeF₂. The processgas may also include a carrier gas such as helium, argon, nitrogen (N₂),etc. Plasma effluents may include ionized or neutral derivatives of theprocess gas and may also be referred to herein as a radical-fluorineprecursor referring to the atomic constituent of the process gasintroduced.

FIG. 3C is a bottom view of a showerhead 1025 for use with a processingchamber in embodiments. Showerhead 1025 corresponds with the showerheadshown in FIG. 3A. Through-holes 1031, which show a view of first fluidchannels 1019, may have a plurality of shapes and configurations tocontrol and affect the flow of precursors through the showerhead 1025.Small holes 1027, which show a view of second fluid channels 1021, maybe distributed substantially evenly over the surface of the showerhead,even amongst the through-holes 1031, which may help to provide more evenmixing of the precursors as they exit the showerhead than otherconfigurations.

The chamber plasma region 1015 or a region in an RPS may be referred toas a remote plasma region. In embodiments, the radical precursor, e.g.,a radical-fluorine precursor, is created in the remote plasma region andtravels into the substrate processing region where it may or may notcombine with additional precursors. In embodiments, the additionalprecursors are excited only by the radical-fluorine precursor. Plasmapower may essentially be applied only to the remote plasma region inembodiments to ensure that the radical-fluorine precursor provides thedominant excitation. Nitrogen trifluoride or another fluorine-containingprecursor may be flowed into chamber plasma region 1015 at rates betweenabout 5 sccm and about 500 sccm, between about 10 sccm and about 150sccm, or between about 25 sccm and about 125 sccm in embodiments.

Combined flow rates of precursors into the chamber may account for 0.05%to about 20% by volume of the overall gas mixture; the remainder beingcarrier gases. The fluorine-containing precursor may be flowed into theremote plasma region, but the plasma effluents may have the samevolumetric flow ratio in embodiments. In the case of thefluorine-containing precursor, a purge or carrier gas may be firstinitiated into the remote plasma region before the fluorine-containinggas to stabilize the pressure within the remote plasma region. Substrateprocessing region 1033 can be maintained at a variety of pressuresduring the flow of precursors, any carrier gases, and plasma effluentsinto substrate processing region 1033. The pressure may be maintainedbetween about 0.1 mTorr and about 100 Torr, between about 1 Torr andabout 20 Torr or between about 1 Torr and about 5 Torr in embodiments.

Embodiments of the deposition systems may be incorporated into largerfabrication systems for producing integrated circuit chips. FIG. 4 showsone such processing system (mainframe) 1101 of deposition, etching,baking, and curing chambers in embodiments. In the figure, a pair offront opening unified pods (load lock chambers 1102) supply substratesof a variety of sizes that are received by robotic arms 1104 and placedinto a low pressure holding area 1106 before being placed into one ofthe substrate processing chambers 1108 a-f. A second robotic arm 1110may be used to transport the substrate wafers from the holding area 1106to the substrate processing chambers 1108 a-f and back. Each substrateprocessing chamber 1108 a-f, can be outfitted to perform a number ofsubstrate processing operations including the dry etch processesdescribed herein in addition to cyclical layer deposition (CLD), atomiclayer deposition (ALD), chemical vapor deposition (CVD), physical vapordeposition (PVD), etch, pre-clean, degas, orientation, and othersubstrate processes.

The substrate processing chambers 1108 a-f may be configured fordepositing, annealing, curing and/or etching a film on the substratewafer. In one configuration, all three pairs of chambers, e.g., 1108a-f, may be configured to etch a film on the substrate, for example,chambers 1108 a-d may be used to etch the gapfill silicon oxide tocreate space for the airgap while chambers 1108 e-f may be used to etchthe polysilicon.

In the preceding description, for the purposes of explanation, numerousdetails have been set forth to provide an understanding of variousembodiments of the present invention. It will be apparent to one skilledin the art, however, that certain embodiments may be practiced withoutsome of these details, or with additional details.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon” or “polysilicon”of the patterned substrate is predominantly Si but may include minorityconcentrations of other elemental constituents such as nitrogen, oxygen,hydrogen and carbon. Exposed “silicon” or “polysilicon” may consist ofor consist essentially of silicon. Exposed “silicon nitride” of thepatterned substrate is predominantly Si₃N₄ but may include minorityconcentrations of other elemental constituents such as oxygen, hydrogenand carbon. “Exposed silicon nitride” may consist essentially of orconsist of silicon and nitrogen. Exposed “silicon oxide” of thepatterned substrate is predominantly SiO₂ but may include minorityconcentrations of other elemental constituents such as nitrogen,hydrogen and carbon. In embodiments, silicon oxide films etched usingthe methods taught herein consist essentially of or consist of siliconand oxygen.

The term “precursor” is used to refer to any process gas which takespart in a reaction to either remove material from or deposit materialonto a surface. “Plasma effluents” describe gas exiting from the chamberplasma region and entering the substrate processing region. Plasmaeffluents are in an “excited state” wherein at least some of the gasmolecules are in vibrationally-excited, dissociated and/or ionizedstates. A “radical precursor” is used to describe plasma effluents (agas in an excited state which is exiting a plasma) which participate ina reaction to either remove material from or deposit material on asurface. “Radical-fluorine” are radical precursors which containfluorine but may contain other elemental constituents. The phrase “inertgas” refers to any gas which does not form chemical bonds when etchingor being incorporated into a film. Exemplary inert gases include noblegases but may include other gases so long as no chemical bonds areformed when (typically) trace amounts are trapped in a film.

The terms “gap” and “trench” are used throughout with no implicationthat the etched geometry has a large horizontal aspect ratio. Viewedfrom above the surface, trenches may appear circular, oval, polygonal,rectangular, or a variety of other shapes. A trench may be in the shapeof a moat around an island of material. The term “via” is used to referto a low aspect ratio trench (as viewed from above) which may or may notbe filled with metal to form a vertical electrical connection. As usedherein, an isotropic or a conformal etch process refers to a generallyuniform removal of material on a surface in the same shape as thesurface, i.e., the surface of the etched layer and the pre-etch surfaceare generally parallel. A person having ordinary skill in the art willrecognize that the etched interface likely cannot be 100% conformal andthus the term “generally” allows for acceptable tolerances.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of thedisclosed embodiments. Additionally, a number of well-known processesand elements have not been described to avoid unnecessarily obscuringthe present invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the dielectric material”includes reference to one or more dielectric materials and equivalentsthereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A method of forming a floating gate, the method comprising:transferring a patterned substrate into a substrate processingmainframe, wherein the patterned substrate comprises two polysiliconfloating gates separated by shallow trench isolation silicon oxidegapfill dielectric, wherein the two polysilicon floating gates each havevertical sidewalls; transferring the patterned substrate into a firstsubstrate processing chamber mounted on the substrate processingmainframe; flowing a fluorine-containing precursor and ahydrogen-containing precursor into a first remote plasma region withinthe first substrate processing chamber while striking a plasma to formfirst plasma effluents from a combination of the fluorine-containingprecursor and the hydrogen-containing precursor; flowing the firstplasma effluents into a first substrate processing region within thefirst substrate processing chamber; wherein the first substrateprocessing region houses the patterned substrate; reacting the firstplasma effluents with the shallow trench isolation silicon oxide gapfilldielectric to form solid residue and sublimating the solid residue;transferring the patterned substrate from the first substrate processingchamber to a second substrate processing chamber mounted on thesubstrate processing mainframe; flowing a fluorine-containing precursorinto a second remote plasma region within the second substrateprocessing chamber while striking a plasma to form second plasmaeffluents and flowing the second plasma effluents through a showerheadinto a second substrate processing region housing the patternedsubstrate within the second substrate processing chamber; isotropicallyetching the two polysilicon floating gates to thin their width and formsidewalls which are again vertical by reacting the second plasmaeffluents with the two polysilicon floating gates; and removing thepatterned substrate from the substrate processing mainframe, wherein thepatterned substrate is not exposed to atmosphere between transferringthe patterned substrate into the substrate processing mainframe andremoving the patterned substrate from the substrate processingmainframe.
 2. The method of claim 1, wherein sublimating the solidresidue comprises raising a temperature of the patterned substrate. 3.The method of claim 1, further comprising depositing a conformalinter-poly dielectric layer after isotropically etching the twopolysilicon floating gates.
 4. The method of claim 1, wherein a sequenceof forming the solid residue and sublimating the solid residue occurs atleast two times.
 5. The method of claim 1, wherein thefluorine-containing precursor is nitrogen trifluoride.
 6. The method ofclaim 1, wherein the hydrogen-containing precursor comprises at leastone of hydrogen (H₂) and ammonia.
 7. The method of claim 1, wherein eachsidewall of the two polysilicon floating gates is within 2° of vertical.8. The method of claim 1, wherein an electron temperature in the secondsubstrate processing region during reacting the second plasma effluentsis below 0.5 eV.
 9. A method of forming a floating gate, the methodcomprising: transferring a patterned substrate into a substrateprocessing mainframe, wherein the patterned substrate comprises twopolysilicon floating gates separated by shallow trench isolation siliconoxide gapfill dielectric, wherein the two polysilicon floating gateseach have vertical sidewalls; transferring the patterned substrate intoa first substrate processing chamber mounted on the substrate processingmainframe; flowing a fluorine-containing precursor into a first remoteplasma region within the first substrate processing chamber whilestriking a plasma to form first plasma effluents; flowing the plasmaeffluents into a first substrate processing region within the firstsubstrate processing chamber; wherein the first substrate processingregion houses the patterned substrate; and flowing an unexcitedprecursor directly into the first substrate processing region withoutfirst passing the unexcited precursor through any plasma prior toentering the first substrate processing region; reacting the plasmaeffluents with the shallow trench isolation silicon oxide gapfilldielectric; transferring the patterned substrate from the firstsubstrate processing chamber to a second substrate processing chambermounted on the substrate processing mainframe; flowing afluorine-containing precursor into a second remote plasma region withinthe second substrate processing chamber while striking a plasma to formsecond plasma effluents and flowing the second plasma effluents througha showerhead into a second substrate processing region housing thepatterned substrate within the second substrate processing chamber;isotropically etching the two polysilicon floating gates to reduce froman initial floating gate width to a final floating gate width and formsidewalls which are again essentially vertical by reacting the secondplasma effluents with the two polysilicon floating gates; and removingthe patterned substrate from the substrate processing mainframe, whereinthe patterned substrate is not exposed to atmosphere betweentransferring the patterned substrate into the substrate processingmainframe and removing the patterned substrate from the substrateprocessing mainframe.
 10. The method of claim 9, wherein the unexcitedprecursor comprises water or an alcohol.
 11. The method of claim 9,wherein the unexcited precursor comprises NxHy where x and y are greaterthan or equal to one.
 12. The method of claim 9, wherein the secondremote plasma region is devoid of oxygen during flowing thefluorine-containing precursor into the second remote plasma region. 13.The method of claim 9, wherein the second remote plasma region is devoidof hydrogen during flowing the fluorine-containing precursor into thesecond remote plasma region.
 14. The method of claim 9, wherein anelectron temperature in the first substrate processing region duringreacting the first plasma effluents and in the second substrateprocessing region during reacting the second plasma effluents are eachbelow 0.5 eV.
 15. The method of claim 9, wherein the final floating gatewidth is less than 80% of the initial floating gate width.